This invention relates to a burner assembly for discharging a mixture of particulate fuel and air to a furnace, and, more particularly, to such an assembly having an inlet elbow for creating a low pressure and an improved fuel/air distribution with a minimum of particle fracturing and wall erosion.
Many burner assemblies that introduce fuel and air into a furnace have a tangential inlet, that is, a duct, or the like, that receives the fuel/air mixture and introduces it tangentially relative to the cylindrical body of the burner. This enables the relatively heavy fuel particles to migrate radially outwardly towards the burner wall due to centrifugal forces, and the relatively light air to tend to pass through the center of the burner, which aids the burner designer in creating optimum combustion conditions at the burner outlet.
However, problems exist in the use of these tangential flow patterns at the burner inlet. For example, if the turn from the inlet duct into the burner body is relatively sharp, the particulate material impinges upon an area of the duct directly opposite its inlet and rapidly erodes the wall in this area as well as cause the particles to fracture and lose energy by friction. Also, the distribution of the fuel/air mixture is less than uniform and the long, curved tangentially-extending pipes are difficult and expensive to install and take up a great deal of space.
Accordingly, U.S. Pat. Nos. 4,387,914 and 5,060,984 each disclose an specially designed elbow designed to receive a fluent material to prevent erosion of the inner surface of the elbow as well as fracture of the fuel particles and frictional losses. However, these elbows are unsuited for use in a combustion system utilizing one or more burners for receiving a mixture of air and fuel, such as coal, and combusting the fuel for several reasons. For example, the design of the elbows disclosed in the above-cited patents is such that the fluent material being processed continuously passes through, and is discharged from, the elbow in a relatively large, single flow stream. As a result, the pressure drop across the elbow is relatively high which, if used in a combustion system, would require relatively high fan capacities and a general increase in the power requirements of the system. Also, the single, relatively large, flow stream of the fuel-air mixture and its associated flame pattern in a combustion system would result in relatively uneven fuel distribution, relatively low flame radiation, relatively high average flame temperature, less than complete combustion and a relatively long residence time of the gas components within the flame, all of which are undesirable from an efficiency standpoint.
Therefore what is needed is a burner assembly utilizing the elbow disclosed in the above-cited patents while eliminating the problems when the elbow is utilized with a burner in a combustion system.